The invention relates to an electron beam generator, especially for an electron gun, having a high-voltage insulator disposed in a casing and bearing an incandescent cathode and a control electrode, both connectable to a high-voltage terminal.
An electron beam generator of the stated kind is disclosed in DE-OS 33 33 686. In electron beam generators of this kind, the high temperature of the incandescent cathode causes extreme heating of the components adjacent it. In the known electron beam generator excessive heating is prevented by disposing coolant passages in the high-voltage insulator which are made of plastic and are cast in place in the casting resin of the high-voltage insulator. To prevent excessive potential drops, the coolant carried through the coolant passages is transformer oil. In a central recess in the high-voltage insulator above the coolant passages there is a capsule of ferromagnetic material containing circuitry for the rectification and filtration of the Wehnelt voltage and cathode heater current.
From the capsule connecting wires run to the cathode and control electrode disposed below the coolant passages. Empty spaces present within the high-voltage insulator are likewise filled with oil to prevent excessive potential drops and faciliate thermal transfer. These known measures for cooling the electron beam generator have proven to be insufficiently effective. The heat passes from the cathode and the control electrode only over comparatively long distances in the high-voltage insulator into the range of the coolant passages and the thermal transfer from the high-voltage insulator to the coolant oil in the coolant passages is poor. The result is a considerable temperature difference, so that the temperature at the cathode holder and the control electrode can exceed the allowable level. Also the transport of heat through the insulating oil within the beam generator does not become effective until higher temperatures are reached, since the natural convection is unable to transport appreciable amounts of heat until the temperature reaches about 130 degrees C. Lastly, in the known electron beam generators the arrangement of the cooling passages proves to be disadvantageous from the construction point of view because it causes the structural height of the beam head to become greater and the connections for the cathode and the control electrode to become longer.